Polyester molding for use with a casing

ABSTRACT

By molding a biodegradable plastic material which is treated with a compound reactive to the active hydrogen in the biodegradable plastic material, a biodegradable plastic material and molding having long-term reliability are obtained.

CROSS REFERENCE TO RELATED APPLICATIONS

The present document claims priority to Japanese Priority DocumentJP2001-208456, filed in the Japanese Patent Office on Jul. 9, 2001, andJapanese Priority Document JP 2002-121889, filed in the Japanese PatentOffice on Apr. 24, 2002, the entire contents of which are incorporatedherein by reference to the extent permitted by law.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a biodegradable plastic material havingimproved durability and, also, a biodegradable plastic molding usingsame.

2. Description of the Related Art

Today, plastics are prevalent in all aspects of daily life and industry,and annual production of plastics all over the world has reachedapproximately one hundred million tons. The greater part thereof isdisposed of after use, and this has been recognized as one of thefactors causing disruption in the global environment. At present,recycling of plastics, as well as using biodegradable polymers, areattracting attention as measures for solving this problem.

With respect to recycling plastics, although the Law for Recycling ofSpecified Kinds of Home Appliances was enacted in Japan in April 2001 inorder to recycle used electric appliances, the recycling of usedelectric appliances has been, at best, inadequate, with the exception offour kinds of large-sized electric appliances including televisions,refrigerators, air conditioners and washing machines. Instead, mostelectric appliances are disposed of as incombustible refuse. Also, whensold in large quantities, even small-sized electric appliances end up ashuge amounts of waste material and present problems in terms ofenvironmental preservation.

Shredding waste material is a popular processing method employed today.However, since shredding merely decreases the volume of waste material,and since the waste material, if buried underground, remains unchangedover several ten years or several hundred years, shredding does notbring any basic solution to this environmental problem. Even if theshredder dust were to be recycled, because it has been finely reduced,valuable material such as copper would become mixed with other lessvaluable material, for example, and its purity would be compromised,thereby lowering collection efficiency.

On the other hand, it could be inferred that using biodegradablepolymers has the following two advantages. First, by manufacturing thecasing and structure of an electronic appliance, both of which occupythe bulk of a product's volume, with biodegradable material, and byemploying an easily separable structure such as, for example, screws orfitting (male-female) structures to assemble these parts withnon-biodegradable parts, such as electronic components and substrates,parts to be recycled and parts which can be disposed of can bedisassembled and processed individually with relative ease. Thus,improved collection efficiency could be expected.

Second, biodegradable material may be used for the external surfaces ofthe casings of products such as radios, microphones, portabletelevisions, keyboards, Walkmans, portable telephones, radio cassetterecorders and earphones, for instance. By thus employing biodegradablematerial for portions of devices which frequently contact a user's bodyas described above, electrical appliances, which are safer than thoseemploying synthetic resins for comparable portions, may be provided.

However, not every kind of biodegradable polymer is suitable for use inthe manner described above, and in order to be suitable for use as amaterial for the casing or structure of an electrical appliance, certainphysical properties are required. The present inventors found that it isat least required that no degradation of the physical properties takeplace even if held for 48 hours in an atmosphere of 80° C. intemperature and 80% humidity.

Biodegradable polymers are organic materials, which are degradable andassimilated into the environment by the action of nature ormicroorganisms, and which have been developed as ideal materials thatmeet environmental needs. Examples of such biodegradable polymersdescribed above may include: polysaccharide derivatives such as, forinstance, cellulose, starch, dextran, chitin and the like; peptides suchas, for example, collagen, casein, fibrin, gelatin and the like;polyamino acids; polyvinyl alcohol; polyamides such as, for example,4-nylon and 2-nylon/6-nylon copolymer; aliphatic polyesters; and soforth.

Aliphatic polyester resin, which is a typical example of a biodegradablepolymer, generally has a low melting point and is inadequate in terms ofits physical properties (particularly, heat resistance and shockresistance) to be fit for use in commercially viable moldings.Considerations such as adding inorganic fillers or crystal nucleicagents for improving the crystallization rate or blending withbiodegradable resins showing rubber-like properties and having low glasstransition points have been made. Several patent applications for suchmoldings using plastics described above have already been filed(Japanese Unexamined Patent Application Publications No. 3-290461, No.4-146952, No. 4-325526 and the like). These moldings are used as filmsor packaging materials, and hence do not specifically requiredurability.

On the other hand, in applying biodegradable aliphatic resin to thecasings of electrical appliances and electronic devices and the like,long-term reliability, in other words, durability under conditions ofconstant temperature and humidity, as well as heat resistance, arerequired. Although product life cycles vary between electric appliancesand electronic devices, in small-sized audio products, it is necessarythat their physical properties be maintained for 3 to 7 years under, forexample, conditions of 30° C. and 80% relative humidity. Considering thefact that electric appliances and electronic devices are operated underwidely varying temperatures and humidity conditions, since existingbiodegradable polyesters have issues in terms of long-term reliability,as described above, they could not be used for casings of electricappliances, electronic devices and the like. Currently, biodegradablepolymers, mainly aliphatic polyester resins, are beginning to be used asmaterials for use in agriculture, forestry and fishery (films, planters,fishing lines, fishing nets and the like), and materials for use incivil engineering (water-retentive sheets, plant nets, sandbags and thelike), as well as in the fields of packaging and containerization (forthose which are hard to recycle due to adhesion of soil and foodthereto).

As described above, it is at least required of biodegradable polyesterresins that no degradation of their physical properties take place forat least 48 hours under conditions of constant temperature and humidity(for instance, at 80° C. and 80% relative humidity) if they are to beused in casings of electric appliances, electronic devices and the like.Moldings of existing biodegradable polyesters, even in the case ofpolylactic acid, for example, which is most resistant to heat, whensubjected to aging tests over 48 hours at a temperature of 80° C. and arelative humidity of 80%, a 60% decrease in molecular weight by theaction of hydrolysis takes place (Refer to Comparative example 1 below),and thus using them as materials for casings of household electricappliances is difficult. As one of the factors accounting for such adegradation in physical properties, that is, the occurrence ofhydrolysis, it is known, for example, in the case of polyester, that acarboxyl group at a polymer chain terminal catalytically causeshydrolysis of ester bonds in molecular chains.

SUMMARY OF THE INVENTION

The present invention sets forth a plastic material, which, in order toensure long-term reliability, maintains its physical properties (such asstrength, hydrolysis resistance and heat resistance, for example) whilethe products are in use by preventing active hydrogen in anactive-hydrogenous functional group, such as carboxyl and hydroxylgroups, and the like, in biodegradable plastics from catalyticallycausing hydrolysis of main chains, and which, when disposed of, ishydrolyzed and is degraded by microorganisms generally found in nature.

It is an aspect of the present invention to provide a biodegradableplastic material capable of ensuring long-term reliability,biodegradable polyester material in particular, and, further, a moldingusing this biodegradable plastic material.

As a result of conducting thorough research to ensure long-termreliability of biodegradable polyesters for use as casing materials inelectric appliances, electronic devices and the like, the presentinventors have found that improvements in long-term reliability areattained by adding a compound reactive to active hydrogen contained inthe biodegradable polyester to make this compound react with the activehydrogen so as to decrease the amount of active hydrogen, andspecifically by thereby reducing the amount of residual fatty acids inthe composition, in other words the acid value, below a predeterminedamount. In addition, the present inventors have also found that theamount of active hydrogen may be reduced in biodegradable polymershaving an amino group and/or an amide bond by treating them in a mannersimilar to biodegradable polyesters.

The term “active hydrogen” as used herein denotes compounds having abond between oxygen, nitrogen or the like and hydrogen, this bond beinghigher in reactivity than a bond between carbon and hydrogen. Examplesof such compounds include, for instance, carboxyl groups: —COOH,hydroxyl groups: —OH, amino groups: —NH₂, amide bonds: —NHCO—, and thelike.

More specifically, the present inventors have found that a casingmaterial having long-term reliability which does not suffer degradationin physical properties after an aging test, for example, over 48 hoursat 80° C. and 80% humidity, by making compounds reactive to activehydrogen, such as carbodiimide compounds and polyisocyanate compounds,react with biodegradable plastic material in order to control the amountof, for example, fatty acids, that is, the acid value at or below apredetermined value. The present inventors conducted further studies,and completed the present invention.

In other words, the present invention relates to:

(1) a biodegradable plastic material treated with a compound reactive tothe active hydrogen contained in biodegradable plastics;

(2) the biodegradable plastic material described above in (1), whereinthe biodegradable plastic material includes a biodegradable polyestermaterial;

(3) the biodegradable plastic material described above in (1), whereinthe biodegradable plastic material includes (a) a copolymer ofbiodegradable polyester and biodegradable polymer having an amino groupand/or an amide bond or (b) a mixture of biodegradable polyester andbiodegradable polymer having an amino group and/or an amide bond;(4) the biodegradable plastic material described above in (1), whereinthe acid value of the biodegradable plastic material treated with acompound reactive to active hydrogen is 0.5 or less;(5) the biodegradable plastic material described above in (1), whereineven after a 48-hour-aging process under a condition of constanttemperature and humidity at 80° C. and 80% relative humidity, the risein acid value is not more than 0.2, and the decrease in molecular weightis 10% or less;(6) the biodegradable plastic material described above in (1), whereinthe active hydrogen is attributable to at least one atomic groupselected from carboxyl groups, hydroxyl groups, amino groups and amidebonds in the biodegradable plastic material;(7) the biodegradable plastic material described above in (1), whereinthe compound reactive to active hydrogen includes a bridging agenthaving a carbodiimide group;(8) the biodegradable plastic material described above in (7), whereinthe bridging agent having a carbodiimide group includesdicyclohexylcarbodiimide or diisopropylcarbodiimide;(9) the biodegradable plastic material described above in (1), whereinthe biodegradable plastic material contains a silicate;(10) the biodegradable plastic material as described above in (9),wherein the silicon dioxide content of the silicate is 50% or more;(11) the biodegradable plastic material described above in (9), whereinthe silicate takes the form of particles having an average diameter ofnot more than 50 μm;(12) a biodegradable plastic molding molded from a biodegradable plasticmaterial treated with a compound reactive to the active hydrogen inbiodegradable plastics;(13) the biodegradable plastic molding described above in (12), whereinthe biodegradable plastic material includes a biodegradable polyestermaterial;(14) the biodegradable plastic molding described above in (12), whereinthe biodegradable plastic material includes (a) a copolymer ofbiodegradable polyester and biodegradable polymer having an amino groupand/or an amide bond or (b) a mixture of biodegradable polyester andbiodegradable polymer having an amino group and/or an amide bond;(15) the biodegradable plastic molding described above in (12), whereinthe biodegradable plastic molding includes a casing for an electricappliance;(16) the biodegradable plastic molding described above in (12), whereinthe acid value of the biodegradable plastic material treated with acompound reactive to active hydrogen is 0.5 or less;(17) the biodegradable plastic molding described above in (12), whereineven after a 48-hour-aging process under a condition of constanttemperature and humidity at 80° C. and 80% relative humidity, the risein acid value is not more than 0.2, and the decrease in molecular weightis 10% or less;(18) the biodegradable plastic molding described above in (12), whereinthe active hydrogen is attributable to at least one atomic groupselected from carboxyl groups, hydroxyl groups, amino groups and amidebonds in the biodegradable plastic material;(19) the biodegradable plastic molding described above in (12), whereinthe compound reactive to active hydrogen includes a bridging agenthaving a carbodiimide group;(20) the biodegradable plastic molding described above in (19), whereinthe bridging agent having a carbodiimide group includesdicyclohexylcarbodiimide or diisopropylcarbodiimide;(21) the biodegradable plastic molding described above in (12), whereinthe biodegradable plastic molding contains a silicate;(22) the biodegradable plastic molding described above in (21), whereinthe silicon dioxide content of the silicate is 50% or more;(23) the biodegradable plastic molding described above in (21), whereinthe silicate takes the form of particles having an average diameter ofnot more than 50 μm;(24) a method of manufacturing a biodegradable plastic molding, whereina compound reactive to active hydrogen is added to and mixed with abiodegradable plastic material before, while or after melting thebiodegradable plastic material, and thereafter the biodegradable plasticmaterial is molded;(25) the method of manufacturing a biodegradable plastic moldingdescribed above in (24), wherein the molding step is performed by meansof film molding, extrusion molding or injection molding;(26) a method of manufacturing a biodegradable plastic molding, whereina silicate and a compound reactive to active hydrogen are added to andmixed with a biodegradable plastic material simultaneously orindividually before, while or after melting the biodegradable plasticmaterial, and thereafter the biodegradable plastic material is molded;(27) the method of manufacturing a biodegradable plastic moldingdescribed above in (26), wherein the molding step is performed by meansof film molding, extrusion molding or injection molding;(28) the method of manufacturing a biodegradable plastic moldingdescribed above in (26), wherein the silicon dioxide content of thesilicate is 50% or more; and(29) the method of manufacturing a biodegradable plastic moldingdescribed above in (26), wherein the silicate takes the form ofparticles having an average diameter of not more than 50 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention disclosed herein will become better understood as adetailed description is made of the preferred embodiments with referenceto the appended drawings in which:

FIG. 1 a is a diagram in which time (days) is plotted againsttemperature (° C.), wherein the rise in acid value was not more than 0.2and the decrease in molecular weight was 10% or less in an example 5described below;

FIG. 1 b is a diagram in which the logarithm of time (log(days)) isplotted against the reciprocal of temperature (1/temperature: 1/K),wherein the rise in acid value was not more than 0.2 and the decrease inmolecular weight was 10% or less in the example 5;

FIG. 2 a is a diagram in which time (days) is plotted againsttemperature (° C.), wherein the rise in acid value was not more than 0.2and the decrease in molecular weight was 10% or less in an example 6described below;

FIG. 2 b is a diagram in which the logarithm of time (log(days)) isplotted against the reciprocal of temperature (1/temperature: 1/K),wherein the rise in acid value was not more than 0.2 and the decrease inmolecular weight was 10% or less in the example 6;

FIG. 3 a is a diagram in which the change in acid value is plottedagainst the time (days) over which physical properties of biodegradablepolyester were maintained at each temperature in the example 6; and

FIG. 3 b is a diagram in which the decrease rate (%) of weight-averagemolecular weight is plotted against the retention time (days) over whichphysical properties of biodegradable polyester were maintained at eachtemperature in the example 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The term “biodegradable plastics” as used herein denotes plastics which,once disposed of, are initially degraded into low-molecular weightcompounds and eventually into water and carbon dioxide by the action ofmicroorganisms found in nature (ISO/TC-207/SC3, Biodegradable PlasticsSociety).

Examples of biodegradable polymers which may be used as materials ofsuch biodegradable plastics include, for instance, polysaccharidederivatives such as cellulose, starch, dextran and chitin; peptides suchas collagen, casein, fibrin and gelatin; polyamino acids; polyvinylalcohol; polyamides such as nylon 4 and nylon 2/nylon 6 copolymer; andpolyesters such as polyglycollic acid, polylactic acid, polysuccinicacid ester, polyoxalic ester, polyhydroxybutyric acid, polydiglycollicacid butylene, polycaprolactone, polydioxanone, and the like. Thus, awide variety of biodegradable polymers are available and may also beused herein. That is, the biodegradable polymer may be any kind ofmaterial as long as it is an organic material which degrades and isassimilated by the action of nature and microorganisms; it is a materialwhich may be considered an ideal match for the environment and mayinclude any material within the aspects of the present inventiondescribed herein. Of these examples, biodegradable polyester isparticularly preferable.

As long as they lie within the aspects of the present invention, thebiodegradable plastics employed herein may include biodegradablepolyesters, copolymers of biodegradable polyester and biodegradablepolymer having an amino group and/or an amide bond, or a mixture ofbiodegradable polyester and biodegradable polymer having an amino groupand/or an amide bond. Examples of biodegradable polymers having an aminogroup and/or an amide bond include, for instance, biodegradablepolyamides such as nylon and polyamino acid and the like.

Biodegradable polyesters employed for the present invention includepolymers having an ester bond such as —CO—O—, in their main chains, andexamples of the biodegradable polyesters used herein include polyestersmetabolized by the action of microorganisms. Of such polyesters,aliphatic polyester resins having formability, heat resistance and shockresistance are preferable.

Examples of the aliphatic polyester resins mentioned above includehydroxycarboxylic acid-type aliphatic polyester resins, such aspolyoxalic ester, polysuccinic acid ester, polyhydroxybutyric acid,polydiglycollic acid butylene, polycaprolactone, polydioxanone, andpolymers of hydroxy acids such as lactic acid, malic acid and glycollicacid, or copolymers of these polymers. Hydroxycarboxylic acid-typealiphatic polyester resins, such as polylactic acids, are preferable.

The biodegradable polyesters employed for the present invention may besynthesized through various kinds of processes including, for instance,(1) the lactide process, (2) polycondensation of polyhydric alcohol andpolybasic acid, (3) intermolecular polycondensation of hydroxycarboxylicacid having both a hydroxyl group and a carboxyl group in the moleculesthereof, and the like.

The lactide process is a process based on ring-opening polymerization ofcyclic diester and lactones corresponding to the cyclic diester.Examples of such cyclic diesters include, for instance, lactide,glycollide and the like; and examples of such lactones include, forinstance, ε-caprolactone, β-propiolactone, γ-butyrolactone,δ-valerolactone and the like.

Examples of polyhydric alcohols which may be used for thepolycondensation of polyhydric alcohol and polybasic acid include, forinstance, ethylene glycol; diethylene glycol; triethylene glycol;propylene glycol; neopentyl glycol; 1,3-butanediol; 1,4-butanediol;1,6-hexanediol and the like. In addition, examples of polybasic acidswhich may be used for the polycondensation typically include, forinstance, aromatic dicarboxylic acids, such as terephthalic acid,isophthalic acid, orthophthalic acid and naphthalene dicarboxylic acid;aliphatic dicarboxylic acids, such as adipic acid, sebacic acid, oxalicacid, succinic acid, succinic anhydride, maleic acid, maleic anhydride,fumaric acid and dimer acid; and alicyclic dicarboxylic acids, such as1,4-cyclohexane dicarboxylic acid. However, since aliphatic polyestersare better suited for the present invention, it is preferable that thepolyhydric alcohol and the polybasic acid, which are materials for thebiodegradable polyester, be aliphatic compounds.

In addition, the intermolecular polycondensation of thehydroxycarboxylic acid having a hydroxyl group and a carboxyl group inits molecules may be obtained through a process of contact dehydrationcondensation of the corresponding hydroxycarboxylic acid. Examples ofsuch hydroxycarboxylic acids include, for instance, aliphatichydroxycarboxylic acids such as lactic acid, 2-hydroxyacetic acid,2-hydroxypropanoic acid, 2-hydroxybutyric acid, 2-hydroxyvaleric acid,2-hydroxyhexanoic acid, 2-hydroxyheptanoic acid, 2-hydroxyoctanoic acid,2-hydroxy-2-methylpropanoic acid, 2-hydroxy-2-methylbutyric acid,2-hydroxy-2-ethylbutyric acid, 2-hydroxy-2-methylvaleric acid,2-hydroxy-2-ethylvaleric acid, 2-hydroxy-2-propylvaleric acid,2-hydroxy-2-butylvaleric acid, 2-hydroxy-2-methylhexanoic acid,2-hydroxy-2-ethylhexanoic acid, 2-hydroxy-2-propylhexanoic acid,2-hydroxy-2-butylhexanoic acid, 2-hydroxy-2-pentylhexanoic acid,2-hydroxy-2-methylheptanoic acid, 2-hydroxy-2-ethylheptanoic acid,2-hydroxy-2-propylheptanoic acid, 2-hydroxy-2-butylheptanoic acid,2-hydroxy-2-pentylheptanoic acid, 2-hydroxy-2-hexylheptanoic acid,2-hydroxy-2-methyloctanoic acid, 2-hydroxy-2-ethyloctanoic acid,2-hydroxy-2-propyloctanoic acid, 2-hydroxy-2-butyloctanoic acid,2-hydroxy-2-pentyloctanoic acid, 2-hydroxy-2-hexyloctanoic acid,2-hydroxy-2-heptyloctanoic acid, 3-hydroxypropanoic acid,3-hydroxybutanoic acid, 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid,3-hydroxyheptanoic acid, 3-hydroxyoctanoic acid,3-hydroxy-3-methylbutanoic acid, 3-hydroxy-3-methylpentanoic acid,3-hydroxy-3-ethylpentanoic acid, 3-hydroxy-3-methylhexanoic acid,3-hydroxy-3-ethylhexanoic acid, 3-hydroxy-3-propylhexanoic acid,3-hydroxy-3-methylheptanoic acid, 3-hydroxy-3-ethylheptanoic acid,3-hydroxy-3-propylheptanoic acid, 3-hydroxy-3-butylheptanoic acid,3-hydroxy-3-methyloctanoic acid, 3-hydroxy-3-ethyloctanoic acid,3-hydroxy-3-propyloctanoic acid, 3-hydroxy-3-butyloctanoic acid,3-hydroxy-3-pentyloctanoic acid, 4-hydroxybutanoic acid,4-hydroxypentanoic acid, 4-hydroxyhexanoic acid, 4-hydroxyheptanoicacid, 4-hydroxyoctanoic acid, 4-hydroxy-4-methylpentanoic acid,4-hydroxy-4-methylhexanoic acid, 4-hydroxy-4-ethylhexanoic acid,4-hydroxy-4-methylheptanoic acid, 4-hydroxy-4-ethylheptanoic acid,4-hydroxy-4-propylheptanoic acid, 4-hydroxy-4-methyloctanoic acid,4-hydroxy-4-ethyloctanoic acid, 4-hydroxy-4-propyloctanoic acid,4-hydroxy-4-butyloctanoic acid, 5-hydroxypentanoic acid,5-hydroxyhexanoic acid, 5-hydroxyheptanoic acid, 5-hydroxyoctanoic acid,5-hydroxy-5-methylhexanoic acid, 5-hydroxy-5-methylheptanoic acid,5-hydroxy-5-ethylheptanoic acid, 5-hydroxy-5-methyloctanoic acid,5-hydroxy-5-ethyloctanoic acid, 5-hydroxy-5-propyloctaonic acid,6-hydroxyhexanoic acid, 6-hydroxyheptanoic acid, 6-hydroxyoctanoic acid,6-hydroxy-6-methylheptanoic acid, 6-hydroxy-6-methyloctanoic acid,6-hydroxy-6-ethyloctanoic acid, 7-hydroxyheptanoic acid,7-hydroxyoctanoic acid, 7-hydroxy-7-methyloctanoic acid,8-hydroxyoctanoic acid and the like, as well as oligomers which may bederived therefrom.

Examples of catalysts which may be used to prepare the hydroxycarboxylicacid-type aliphatic polyester resins include tin compounds, antimonycompounds, zinc compounds, titanium compounds, iron compounds andaluminum compounds.

Of these, tin and aluminum type catalysts are preferred, and, further,tin octylic acid and aluminum acetylacetonato are particularlypreferable.

Of the hydroxycarboxylic acid-type aliphatic polyester resins above,poly-L-lactic acid prepared through lactide ring-opening condensation isparticularly preferable, since it is hydrolyzed into L-lactic acid, andsince its safety is confirmed. However, it is to be understood that thehydroxycarboxylic acid-type aliphatic polyester resins used herein arenot limited thereto, and, therefore, the lactide used in the manufacturethereof is not limited to L-forms either.

For the compounds reactive to active hydrogen according to the presentinvention, for instance, compounds such as carbodiimide compounds,isocyanate compounds or oxazoline compounds may be employed, all ofwhich show reactivity to the hydrogen in the hydroxyl group and thecarboxyl group, which are terminal functional groups of polyesterresins, or the hydrogen in the amino group and/or amide bond of thebiodegradable polymer, which are contained as copolymers or mixtures.Carbodiimide compounds are particularly suitable, because they melt andblend with polyesters, and because hydrolyzation can be regulated by asmall amount of addition thereof. Also, these compounds are reactive toactive hydrogen and may be used individually or in combinations of twoor more.

The carbodiimide compounds include bridging agents having a carbodiimidegroup and compounds (including polycarbodiimide compounds) having one ormore carbodiimide bonds, such as —N═C═N—, in their molecules. A methodof preparation thereof includes those processes in which, for instance,various kinds of polyisocyanates are subjected to a decarboxylationcondensation reaction at a temperature of about 70° C. or above withouta solvent or in an inert solvent (such as hexane, benzene, dioxane andchloroform) using, as the catalyst, organic phosphorus compounds (suchas O, O-dimethyl-O-(3-methyl-4-nitrophenyl) phosphorothioate, O,O-diethyl-O-(3-methyl-4-(methylthio)phenyl) phosphorothioate andO,O-diethyl-O-2-isopropyl-6-methylpyrimidine-4-isophosphorothioate) ororganic metallic compounds (such as rhodium complex, titanium complex,tungsten complex and palladium complex, and the like).

Examples of monocarbodiimide compounds contained in the carbodiimidecompound above include dicyclohexyl-carbodiimide;diisopropylcarbodiimide; dimethyl-carbodiimide; diisobutylcarbodiimide;dioctylcarbodiimide; t-butylisopropylcarbodiimide; diphenylcarbodiimide;di-t-butylcarbodiimide; di-β-naphthylcarbodiimide and the like. Of theexamples above, dicyclohexylcarbodiimide or diisopropylcarbodiimide areparticularly preferable because of their industrial availability.

Examples of polyisocyanate compounds include, for instance,2,4-tolylenediisocyanate; 2,6-tolylene-diisocyanate;m-phenylenediisocyanate; p-phenylene-diisocyanate;4,4′-diphenylmethanediisocyanate; 2,4′-diphenylmethanediisocyanate;2,2′-diphenylmethane-diisocyanate;3,3,-dimethyl-4,4′-biphenylenediisocyanate;3,3′-dimethoxy-4,4′-biphenylenediisocyanate;3,3′-dichloro-4,4′-biphenylenediisocyanate;1,5-naphthalene-diisocyanate; 1,5-tetrahydronaphthalenediisocyanate;tetramethylenediisocyanate; 1,6-hexamethylenediisocyanate;dodecamethylenediisocyanate; trimethylhexamethylene diisocyanate;1,3-cyclohexylenediisocyanate; 1,4-cyclo hexylenediisocyanate;xylylenediisocyanate; tetramethyl xylylenediisocyanate; hydrogenatedxylylenediisocyanate; lysinediisocyanate; isophoronediisocyanate;4,4′-dicyclo-hexylmethanediisocyanate;3,3′-dimethyl-4,4′-dicyclohexylmethanediisocyanate and the like.Commercially available polyisocyanate compounds are used in examples, aswill be described later, according to the present invention, andaromatic isocyanate adducts, such as Coronate (produced by NipponPolyurethane Industry Co., Ltd.: hydrogenateddiphenylmethanediisocyanate) or Millionate (produced by NipponPolyurethane Industry Co., Ltd.), may be used. However, in the case ofmelt blending, solid polyisocyanate compounds, such as those in which anisocyanate group is blocked with a masking agent (such as polyhydricaliphatic alcohol and aromatic polyol, or the like), are preferred toliquid polyisocyanate compounds.

Examples of oxazoline compounds include, for instance,2,2′-o-phenylenebis(2-oxazoline); 2,2′-m-phenylenebis(2-oxazoline);2,2′-p-phenylenebis(2-oxazoline);2,2′-p-phenylenenbis(4-methyl-2-oxazoline);2,2′-m-phenylenebis(4-methyl-2-oxazoline);2,2′-p-phenylenebis(4,4′-dimethyl-2-oxazoline);2,2′-m-phenylenebis(4,4′-dimethyl-2-oxazoline);2,2′-ethylenebis(2-oxazoline); 2,2′-tetramethylenebis(2-oxazoline);2,2′-hexamethylenebis(2-oxazoline); 2,2′-octamethylenebis(2-oxazoline);2,2′-ethylenebis(4-methyl-2-oxazoline); 2,2′-diphenylenebis(2-oxazoline)and the like.

In treating biodegradable plastics with compounds that are reactive tothe active hydrogen in biodegradable plastics, the compounds that arereactive to active hydrogen are normally added to the biodegradableplastics before, while or after melting the biodegradable plastics, andthey are then blended together. It is preferred that the amount ofcompounds that are reactive to active hydrogen to be added be about 0.1to 5 weight % of the biodegradable plastic. However, since the long-termreliability and the speed of degradation after disposal of thebiodegradable plastic material of the present invention that is treatedwith a compound which is reactive to active hydrogen may be adjusted byvarying the kind and amount of the compound to be added mentioned above,the kind and amount of compound to be added may be determined accordingto the final product to which the biodegradable plastic material is tobe applied. In addition, the compound that is reactive to activehydrogen may be used individually or in combinations of two or morecompounds.

As described above, the biodegradable plastic and the compound reactiveto active hydrogen may be blended before, while or after melting thebiodegradable plastic. That is, blending may be performed at anytime aslong as the biodegradable plastic melts and sufficiently blends with thecompound reactive to active hydrogen.

A method of determining the quantity of active hydrogen contained in thebiodegradable plastic treated with the compound reactive to activehydrogen includes, for instance, measuring the amount of residual fattyacids, that is, the acid value. In the present invention, biodegradablepolyester is a main material, and in the biodegradable polyester thereexist carboxyl groups and hydroxyl groups. Measuring the acid value isequivalent to determining the amount of carboxyl groups in thebiodegradable polyester and is, hence, practically equivalent todetermining the amount of active hydrogen. The term “acid value” denotesthe amount of potassium hydroxide, in milligrams, required to neutralizethe free fatty acid contained in 1 g of fat, such as fatty acids. Adescription of one preferred embodiment of how to measure the acid valuewill now be given.

As reagents for measuring the acid value, a 0.02NKOH-EtOH solution (KOHrepresents potassium hydroxide, and EtOH represents ethanol. The sameshall apply hereinafter), a phenolphthalein solution and a phenol redsolution are used. Methods of preparing each solution are describedbelow.

One preferred method of preparing the 0.02N KOH-EtOH solution is asfollows. Dissolve approximately 0.35 g of potassium hydroxide (KOH) in 5ml of ion exchange water, add EtOH to such that there is now 250 ml ofthe solution, then place the solution in a container tightly sealed witha glass or rubber stopper, and allow the solution to stand for 24 hours.A clear supernatant liquid thus prepared is immediately decanted into adifferent light-shielded container, which is then tightly sealed with arubber stopper and stored. Then, standardization of this regent isconducted using a 0.02N hydrochloric acid. Exactly 5 ml of the 0.02Nhydrochloric acid is measured, 10 ml of ion exchange water is addedthereto, and to this mixture are added, for instance, two drops ofphenolphthalein reagent as an indicator. The prepared 0.02N KOH-EtOHsolution is titrated therewith until it turns light red, and the factorthen is calculated.

One preferred method of preparing the phenolphthalein solution includesdissolving 0.025 g of phenolphthalein in 22.5 ml of EtOH (95%) andadding ion exchange water to obtain 25 mL of the solution. This reagentis colorless at a pH of 8.3 and below, and it turns red at a pH of 8.3to 10.0.

One preferred method of preparing the phenol red solution includesdissolving 0.025 g of phenol red in 5 ml of EtOH (95%) and adding ionexchange water to obtain 25 mL of the solution. This reagent assumes ayellow color at a pH of 6.8 or below, and it turns red at a pH of 8.4 orabove.

One preferred embodiment of measuring the acid value using the preparedreagent includes the following. Exactly 0.1 mg of, for example,polylactic acid as a biodegradable polyester material is weighed and isdissolved in 10 ml of chloroform, and 10 ml of benzyl alcohol is addedthereto. Phenol red is used as an indicator, and the end point is set tobe the point where the 0.02N KOH-EtOH solution changes from yellow tolight red. The volume thereof is expressed as Vml.

Similarly, measurements are taken with a blank solution of 10 ml ofbenzyl alcohol+10 ml of chloroform. The volume thereof is expressed asV₀ ml.

The weight (mg) of KOH required to neutralize the free fatty acidcontained per gram of a sample may be calculated with the followingequation.AV(acid value)={(V−V ₀)×0.02×F×56.11}/S

F in the equation above represents the factor of the 0.02N KOH-EtOHsolution, V is the volume (ml) of the 0.02N KOH-EtOH solution used intitrating the sample, V₀ is the volume (ml) of the 0.02N KOH-EtOHsolution used in titrating the blank solution, and S is the weight (g)of the sample.

In addition, an alternative method of determining the amount of activehydrogen contained in the biodegradable plastic prepared by treatmentwith a compound reactive to active hydrogen includes allowing the activehydrogen to react with Grignard reagents. Because this process, unlikethe previous process, can measure not only the amount of carboxylgroups, but also the amount of hydroxyl groups, amino groups and thelike, it may also be applied to copolymers or mixtures of polyester andpolyamide. Active hydrogen generates methane gas in a quantitativereaction to methylmagnesium iodide. By having this reaction take placein a reaction container of an apparatus for determining the amount ofactive hydrogen, and by collecting the generated methane gas in a gasburet and measuring the volume thereof, the amount of active hydrogencan be determined. Examples of Grignard reagents include, for instance,phenylmagnesium bromide, ethylmagnesium chloride, propylmagnesiumchloride, butylmagnesium chloride and the like, in addition tomethylmagnesium iodide, mentioned above.

It is preferred that the acid value of the biodegradable plasticmaterial prepared through treatment with a compound reactive to activehydrogen be about 0.5 or less prior to the aging process. When the acidvalue is about 0.5 or less, hydrolysis of the biodegradable plastic bythe action of the active hydrogen is less likely to occur, and thus abiodegradable plastic material which can stand 48-hours of aging under acondition of constant temperature and humidity at 80° C. and 80%,respectively, may be obtained.

It is preferable that the rise in acid value in the biodegradableplastic material prepared through treatment with a compound reactive toactive hydrogen after aging be about 0.2 or less. It is also preferablethat the decrease in molecular weight thereof be 10% or less. So long asthe rise in acid value and the decrease in molecular weight are heldwithin their respective ranges, long-term reliability of thebiodegradable plastic material when used as a material for the casingsof electric appliances may be ensured.

The biodegradable plastic material according to the present inventionmay simultaneously use reinforcements, inorganic or organic fillers,antioxidants, thermal stabilizers and ultraviolet absorbers, as well aslubricants, waxes, colorants, crystallization promoters and degradableorganic matters, such as starch, as long as the acid value prior toaging does not exceed 0.5. In addition, they may be used individually orin combination.

Examples of the reinforcements mentioned above include, for instance,glass micro-beads, carbon fibers, chalk, silicates such as asbestos,feldspars, micas, talc, wollastonite, and quartz including novoculite,kaolin and the like. Examples of the inorganic fillers mentioned aboveinclude, in addition to carbon and silicon dioxide, for instance, fineparticles of metal oxides such as alumina, silica, magnesia and ferrite,silicates such as talc, micas, kaolin, zeolite and the like, fineparticles of barium sulfate, calcium carbonate, fullerene and the like.Examples of the organic fillers mentioned above include, for instance,epoxy resins, melamine resins, urea resins, acrylic resins, phenolicresins, polyimide resins, polyamide resins, polyester resins, Teflon(registered trademark) and the like. Of these, carbon and silicondioxide are preferable. The above fillers may also be used individuallyor as a mixture of two or more fillers. The silicates, as inorganicfillers, also function as flame retardants. To be suitable as inorganicfillers, silicates having a silicon dioxide content of approximately 50%or above are preferable. This is because the silicates are extractedfrom natural minerals, and a certain amount of matters other thansilicates (for instance, MgO, CaO, Fe₂ O₃ and Al₂O₃ or the like) areinevitably found. It is to be understood that it is preferable that theeffectiveness of the inorganic fillers as flame retardants not beinhibited by impurities.

In the present invention, the additives described above are not limitedto any specific shape or form, but it is preferable that they take theform of particles. The diameter thereof may be selected according to thespecific kind of additive. For example, in using silicates as theinorganic filler, it is preferable that the average diameter of theparticles thereof obtained by laser diffraction be about 50 μm or less.In this case, the distribution of diameter is of little importance.

Examples of the antioxidants mentioned above include, for instance,phenolic antioxidants, amine antioxidants, phosphoric antioxidants,sulfuric antioxidants, hydroquinone antioxidants, quinoline antioxidantsand the like. Examples of the phenolic antioxidants include: hinderedphenols, for instance, C₂₋₁₀ alkylenediol-bis[3-(3,5-di-branched C₃₋₆alkyl-4-hydroxyphenyl)propionate], such as 2,6-di-t-butyl-p-cresol,1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene,2,2′-methylenebis(4-methyl-6-t-butylphenol),4-4′-methylenebis(2,6-di-t-butylphenol),4,4′-butylidenebis(3-methyl-6-t-butylphenol) and1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], andthe like; di or trioxyC₂₋₄ alkylenediol-bis[3-(3,5-di-branched C₃₋₆alkyl-4-hydroxyphenyl)propionate], such astriethyleneglycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate]and the like; C₃₋₈alkanetriol-bis[3-(3,5-di-branched C₃₋₆alkyl-4-hydroxyphenyl)propionate], such as glyceroltris[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] and the like; C₄₋₈alkanetetraoltetrakis[3-(3,5-di-branched C₃₋₆alkyl-4-hydroxyphenyl)propionate] such aspentaerythritoltetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]and the like; n-octadecyl-3-(4′,5′-di-t-butylphenol)propionate;n-octadecyl-3-(4′-hydroxy-3′,5′-di-t-butylphenol)propionatestearyl-2-(3,5-di-t-butyl-4-hydroxyphenol)propionate;distearyl-3,5-di-t-butyl-4-hydroxybenzylphosphonate;2-t-butyl-6-(3-t-butyl-5-methyl-2-hydroxybenzyl)-4-methylphenylacrylate;N,N′-hexamethylenebis(3,5-di-t-butyl-4-hydroxy-hydrocinnamide);3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane;4,4′-thiobis (3-methyl-6-t-butylphenol);1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenol)butane and the like.Examples of the amine antioxidants mentioned above include, forinstance, phenyl-1-naphthylamine; phenyl-2-naphthylamine;N,N′-diphenyl-1,4-phenylenediamine;N-phenyl-N′-cyclohexyl-1,4-phenylenediamine and the like. Examples ofthe phosphoric antioxidants include, for instance, phosphite compounds,such as triisodecylphosphite, triphenylphosphite,trisnonylphenylphosphite, diphenylisodecylphosphite,phenyldiisodecylphosphite,2,2-methylenebis(4,6-di-t-butylphenyl)octylphosphite,4,4′-butylidenebis(3-methyl-6-t-butylphenyl)ditridecylphosphite,tris(2,4-di-t-butylphenyl)phosphite,tris(2-t-butyl-4-methylphenyl)phosphite, tris(2,4-di-t-amylphenyl)phosphite, tris(2-t-butylphenyl)phosphite,bis(2-t-butylphenyl)phenylphosphite,tris[2-(1,1-dimethylpropyl)-phenyl]phosphite,tris[2,4-(1,1-dimethylpropyl)-phenyl]phosphite, tris(2-cyclohexylphenyl)phosphite, tris(2-t-butyl-4-phenylphenyl)phosphite,and the like, phosphine compounds such as triethylphosphine,tripropylphosphine, tributylphosphine, tricyclohexylphosphine,diphenylvinylphosphine, allyldiphenylphosphine, triphenylphosphine,methylphenyl-p-anisylphosphine, p-anisyldiphenylphosphine,p-tolyldiphenylphosphine, di-p-anisylphenylphosphine,di-p-tolylphenylphosphine, tri-m-aminophenylphosphine,tri-2,4-dimethylphenylphosphine, tri-2,4,6-trimethylphenyl phosphine,tri-o-tolylphosphine, tri-m-tolylphosphine, tri-p-tolylphosphine,tri-o-anisylphosphine, tri-p-anisylphosphine, 1,4-bis(diphenylphosphino)butane and the like. Examples of the hydroquinone antioxidants mentionedabove include, for instance, 2,5-di-t-butylhydroquinone and the like.Examples of the quinoline antioxidants mentioned above include, forinstance, 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline and the like;and examples of the sulfuric antioxidants mentioned above include, forinstance, dilauryl thiodipropionate; distearyl thiodipropionate and thelike. Of the examples above, preferable antioxidants include thephenolic antioxidants (particularly, the hindered phenols), forinstance, polyol-poly [(branched C₃₋₆ alkyl group and hydroxyl groupsubstituted phenyl)propionate] or the like. In addition, theantioxidants may be used individually or in combinations of two or moreantioxidants.

Examples of the thermal stabilizers mentioned above include, forinstance, nitrogenous compounds (for example, basic nitrogenouscompounds such as polyamide, poly-β-alanine copolymers, polyacrylamide,polyurethane, melamine, cyanoguanidine and melamine-formaldehydecondensates), alkalies or alkaline earth metallic compounds (morespecifically, organic carboxylic acid metallic salts (such as calciumstearate, 12-calcium hydroxystearate, and the like)), metal oxides (suchas magnesium oxide, calcium oxide, aluminum oxide and the like), metalhydroxides (such as magnesium hydroxide, calcium hydroxide, aluminumhydroxide and the like), metal carbonates and on the like], zeolite,hydrotalcite and the like. Particularly, of the examples above, alkaliesor alkaline earth metallic compounds (specifically, the alkaline earthmetallic compounds such as magnesium compounds and calcium compounds,and the like), zeolite and hydrotalcite are preferred. In addition, thethermal stabilizers may be used individually or in combinations of twoor more kinds.

The ultraviolet absorbers mentioned above include those of abenzophenone type, a benzotriazole type, a cyanoacrylate type, asalicylate type, an anilide oxalate type and the like. For instance, theultraviolet absorbers include:[2-hydroxy-4-(methacryloyl-oxyethoxy)benzophenone]-methyl methacrylatecopolymers; [2-hydroxy-4-(methacryloyloxymethoxy)benzophenone]-methylmethacrylate copolymers;[2-hydroxy-4-(methacryloyl-oxyoctoxy)benzophenone]-methyl methacrylatecopolymers; [2-hydroxy-4-(methacryloyloxydodecyloxy)benzophenone]-methylmethacrylate copolymers;[2-hydroxy-4-(methacryloyl-oxybenziloxy)benzophenone]-methylmethacrylate copolymers;[2,2′-dihydroxy-4-(methacryloyloxyethoxy)benzophenone]-methylmethacrylate copolymers;[2,2′-dihydroxy-4-(methacryloyloxymethoxy)benzophenone]-methylmethacrylate copolymers;[2,2′-dihydroxy-4-(methacryloyloxyoctoxy)benzophenone]-methylmethacrylate copolymers; and the like. In addition, the ultravioletabsorbers may be used individually or in combinations of two or morekinds.

Examples of the lubricants mentioned above include, for instance:petroleum lubricants, such as liquid paraffin and the like; syntheticlubricants, such as hydrocarbon halide, diester oil, silicone oil andfluorine silicone; various kinds of modified silicone oils such asepoxy-modified, amino-modified, alkyl-modified and polyether-modifiedsilicone oils and the like; silicone lubricating matters, such ascopolymers of an organic compound, such as polyoxy-alkyleneglycol andsilicone, and the like; silicone copolymers; various kinds of fluoricsurfactants, such as fluoroalkyl compounds and the like; fluoriclubricating matters, such as trifluoromethylenechloride low-gradepolymers and the like; waxes, such as paraffin wax and polyethylene waxand the like; higher aliphatic alcohol; higher aliphatic amides; higherfatty acid esters; higher fatty acid salts; molybdenum disulfides; andthe like. Of these, the use of silicone copolymers (copolymers in whichsilicone is block or graft copolymerized with resin) is particularlypreferable. These silicone copolymers include any copolymer in whichsilicone is copolymerized with acrylic resin, polystyrene resin,polynitryl resin, polyamide resin, polyolefin resin, epoxy resin,polybutyral resin, melamine resin, vinyl chloride resin, polyurethaneresin, polyvinyl ether resin or the like. It is preferred that siliconegraft copolymers be used. These lubricating matters may be usedindividually or in combinations of two or more kinds.

Examples of the waxes mentioned above include, for instance: paraffinwaxes and olefin waxes, such as polypropylene wax and polyethylene wax;Fischer-Tropsch waxes; micro-crystalline waxes; montan waxes; fatty acidamide waxes; higher aliphatic alcohol waxes; higher fatty acid waxes;fatty acid ester waxes; carnauba waxes; rice waxes; and the like. Thesewaxes may be used individually or in combinations of two or more waxes.

Examples of the colorants mentioned above include inorganic pigments,organic pigments, dyes and the like. Examples of organic pigmentsinclude, for instance: chromic pigments, cadmium pigments, ironpigments, cobalt pigments, ultramarine, Prussian blue and the like. Inaddition, examples of organic pigments and dyes include, for instance:carbon black; phthalocyanine pigments, such as copper phthalocyanine;quinacridone pigments, such as quinacridone magenta and quinacridonered; azo pigments, such as hansa yellow, disazo yellow, permanentyellow, permanent red and naphthol red; nigrosine dyes such as spiritblack SB, nigrosine base and oil black BW; oil blue; alkali blue and thelike. These colorants may be used individually or in combinations of twoor more colorants.

Examples of the crystallization promoters mentioned above include, forinstance: organic acid salts, such as p-t-butylic sodium benzoate,sodium montanate, calcium montanate, sodium palmitate, calcium stearateand the like; inorganic salts, such as calcium carbonate, calciumsilicate, magnesium silicate, calcium sulfate, barium sulfate, talc andthe like; and metal oxides, such as zinc oxide, magnesium oxide andtitanium oxide and the like. These crystallization promoters may be usedindividually or in combinations of two or more promoters.

A biodegradable plastic molding may be obtained by molding thebiodegradable plastic material as used herein. The biodegradable plasticmolding thus obtained may be used for casings of electric appliancessuch as radios, microphones, televisions, keyboards, portable audioplayers and personal computers and the like, for instance.

The biodegradable plastic material of the present invention may be usedas a material for manufacturing, for example, casings of electricappliances, according to known methods of manufacture. Depending on thekind of product to be molded, a suitable means may be selected frompublicly known means for molding. Examples of molding methods include,for instance, film molding, extrusion molding, injection molding and thelike. Injection molding is particularly preferable. Extrusion molding orinjection molding may be performed in accordance with typical methodsusing publicly known extruders such as uniaxial extruders, multiaxialextruders and tandem extruders, or publicly known injection moldingmachines, such as inline screw-type injection molding machines,multilayer injection molding machines and double headed injectionmolding machines, thereby molding the biodegradable plastic materialinto the desired shape.

One preferred method of molding is as follows. Mix the biodegradableplastic with a compound reactive to active hydrogen in a Henshell mixerof approximately 20 L at about 500 rpm for roughly two minutes. Thenmelt and blend this mixture with a biaxial extruder, which is adjustedto approximately 220° C. to prepare a pellet. This pellet is used tomanufacture, for instance, casings of electric appliances in accordancewith common procedures.

EXAMPLES

Examples using a biodegradable polyester according to the presentinvention will now be described below. However, it is to be understoodthat the present invention is not limited to these examples.

In addition, the molecular weight in the examples is the weight averagemolecular weight (polystyrene reduced molecular weight), and it wasmeasured by Gel permeation chromatography (GPC).

Apparatus: MILLPORE Waters600E system controller

Sensors: UV (Waters484) and RI (Waters410)

Standard sample: Polystyrene

A test sample in chloroform was dissolved such that the concentration ofthe chloroform became 0.15 weight %, and the solution was stirred forapproximately two hours and thereafter filtrated with a Φ0.25 μm filterto prepare the sample.

Example 1

To polylactic acid (brand name: LACEA H100J, product of MitsuiChemicals, Inc.) was added 1 weight % of carbodiimide (brand name:carbodilite 10B, product of Nisshinbo Industries, Inc.) as a compoundreactive to active hydrogen, and the mixture was blended at atemperature of 185° C. for five minutes. The acid value fell from 1.8 to0.1. The blended substance was molded into the shape of a square platewith sides measuring five centimeters each and a thickness of 1 mm, andit was then subjected to aging for 48 hours under a condition of 80° C.in temperature and 80% in humidity. The rise in acid value was 0.2 orless, and the decrease in molecular weight was 10% or less.

Example 2

A sample piece was prepared in a manner similar to that of example 1,except that the amount of carbodiimide added was changed to 0.5 or 0.8weight %, and the mixture was then blended. Upon the addition of 0.5weight % or 0.8 weight % of carbodiimide, the acid value was 0.8 or 0.5,respectively. After being subjected to aging for 48 hours under acondition of 80° C. in temperature and 80% in humidity, the rise in acidvalue of the test sample to which 0.8 weight % of carbodiimide was addedwas 0.2 or less and the decrease in molecular weight was 10% or less. Onthe other hand, with the test sample to which 0.5 weight % ofcarbodiimide was added, the acid value increased from 0.8 to 5.2 in acidvalue and the molecular weight decreased by 60%.

Example 3

To each of polycaprolactone (brand name: Cellgreen, Grade: PH, productof Daicel Chemical Industries, Ltd.) and polybutylene succinate (brandname: Bionolle #1000, product of Showa Highpolymer Co., Ltd.) was added1 weight % of carbodiimide (brand name: Carbodilite 10B, product ofNisshinbo Industries, Inc.) to prepare test samples in a manner similarto that of the previously described example 1. The acid values of thesetest samples were respectively 0.4 and 0.2. Aging of these test sampleswas performed over 48 hours at 80° C. and 80% humidity, wherein the risein acid value and the decrease in molecular weight were 0.2 or less and10% or less, respectively, for both samples.

Example 4

Instead of carbodiimide, 1 weight % of block-type polyurethane (brandname: of Millionate MS50, amount of isocyanate group: 15%, product ofNippon Polyurethane Industry Co., Ltd.) was added to polylactic acid toprepare a test sample in a manner similar to that of the previouslydescribed example 1. The acid value fell to 0.2. Aging of this testsample was performed at 80° C. and at 80% humidity over 48 hours, andthe rise in acid value was 0.2 or less, while the decrease in molecularweight was 10% or less.

Example 5

The test sample in the previously described example 1 was subjected toaging at a constant humidity of 80% and variable temperatures of 85, 80,75, 70 and 65° C., and the changes in acid value, as well as inmolecular weight, were measured. At 85° C., no change occurred up to 48hours. However, after 72 hours elapsed, the acid value rose to 0.3, andafter 96 hours, the acid value increased to 5.1, and the molecularweight decreased by 60%. Thus, this showed that aging for three days at85° C. results in a rise in acid value of not more than 0.2 and adecrease in molecular weight of 10% or less. Similarly, the rise in acidvalue was 0.2 or less, and the decrease in molecular weight was 10% orless for 5 days at 80° C., for eight days at 75° C., for 14 days at 70°C., for 20 days at 65° C.

FIG. 1A is a diagram in which the time (days) and the temperature overand at which, based on the results of the example 5 above, the rise inacid value was 0.2 or less and the decrease in molecular weight was 10%or less are plotted against each other. It is also known that thelogarithm of the reaction rate is proportional to the reciprocal oftemperature (1/temperature) (the Arrhenius equation), and FIG. 1B plotsthe reciprocal of temperature (1/temperature) against the logarithm oftime (Arrhenius plot) according to the Arrhenius theory. This plotrepresents a linear relation, and from the gradient and intercept, arelational expression of the temperature and the time it takes untilchanges in acid value and molecular weight are observed can be obtainedas follows:t=(10^(5070×(1/273.15+temperature(° C.)−13.664))/365wherein t represents the time (years) it takes to observe a change inacid value and in molecular weight.

According to this equation, the time it takes to observe a rise in acidvalue and a decrease in molecular weight when subjected to aging at 30°C. and 80% humidity was 3.2 years. Thus, as long as a compound reactiveto active hydrogen is added and the acid value is controlled at or below0.5, it may be expected that physical properties may be maintained forat least 3 years in an environment of 30° C. and 80% relative humidity.

Example 6

An experiment similar to that described in the previously noted example5 was conducted, except that the amount of carbodiimide added waschanged to 2 weight %. FIG. 2A is, like FIG. 1A, a diagram plotting thetime (days) and temperature over and at which the rise in acid value is0.2 or less while the decrease in molecular weight is 10% or less. FIG.2B is an Arrhenius plot diagram, similar to FIG. 1B. This plot, as withthat of FIG. 1B, represents a linear relation, and from the gradient andintercept, a relational expression of the temperature and the time ittakes until changes in acid value and molecular weight are observed canbe obtained as follows;t=(10^(5312×(1/273.15+temperature(° C.)−14.065))/365wherein t represents the time (years) it takes to observe changes inacid value and molecular weight.

According to this equation, the time it takes to observe a rise in acidvalue and a decrease in molecular weight when subjected to aging at 30°C. and 80% humidity was 7.9 years. Thus, as long as the initial acidvalue is kept at or below 0.5, and the added amount of the compoundreactive to active hydrogen is double that of the example 5, it may beexpected that it is possible to maintain physical properties for 8 yearsunder the same aging conditions as those in the previously describedexample 1. In other words, it was found that the terms during whichphysical properties can be guaranteed may be set to suit differingproduct lives by adjusting the added amount of the compound reactive toactive hydrogen.

With respect to each of the samples in the example 6 above, in FIGS. 3Aand 3B, changes in acid value and in molecular weight, respectively,when subjected to aging at various temperatures and at 80% humidity, areplotted against time. From the example 6, it was found that the terms ofguarantee of the physical properties can be set to suit the differinglives of commercial products by adjusting the amount of additives.Further, as seen in FIGS. 3A and 3B, it also was found that after acertain period had elapsed, hydrolysis accelerated and desirablebiodegradability was observed. Further, this hydrolysis was equivalentto that of biodegradable polyesters in which no compound reactive toactive hydrogen is present. In other words, it was found that thephysical properties may be maintained for the duration of use, whileonce a period during which physical properties are maintained expires, abiodegradability equivalent to that of biodegradable polyesters may beelicited.

Comparative Example 1

As was done in example 1 above, two kinds of polylactic acids (productsof Mitsui Chemicals, Inc. and Shimadzu Corporation) to which nocompounds reactive to active hydrogen were added were subjected to agingunder the same conditions as those in the example 1. Their acid valueswere 1.8 each. Subsequent to aging, their molecular weight decreased by60%, and their flexural strengths dropped to 1/10 th the initial value;and thus, they were not at all suitable for use in molding casings.

Comparative Example 2

Without adding any compounds reactive to active hydrogen, thepolycaprolactone (brand name: Cellgreen, Grade: PH, product of DaicelChemical Industries, Ltd.) and polybutylene succinate (brand name:Bionolle #1000, product of Showa Highpolymer Co., Ltd.) used in thepreviously described example 3 were blended in a manner similar to thatof the previously described example 1. Aging of these blended samplesunder the same conditions as those of the previously described example 1(at 80° C. and 80% humidity over 48 hours) caused an 80% decrease inmolecular weight. Thus, they were not at all suitable for use in moldingcasings.

As described above, the biodegradable plastic material of the presentinvention is a plastic which does not use fossil material and which isbiodegradable. Specifically, it is a composition which secures thestability (for three years at 30° C. and 80% humidity) of biodegradablepolyesters, and it may be applied to casings of electric appliances andcomputers which require durability. The biodegradable plastic molding,after the term during which stability is secured lapses, showshydrolytic properties equivalent to those observed in the absence ofcompounds reactive to active hydrogen, and it is degraded in culturesolutions or soil containing microorganisms and eventually disappears.Accordingly, it is possible to reduce the volume of waste. Thebiodegradable plastic molding is also useful because it can bemanufactured through simple operations.

The preferred embodiments described herein are illustrative and notrestrictive, the scope of the present invention being indicated by theappended claims, and all variations which come within the meaning of theclaims are intended to be embraced therein.

1. A biodegradable plastic material treated with a compound reactive toactive hydrogen contained in said biodegradable plastic material;wherein said biodegradable plastic material comprises apolycaprolactone; wherein said biodegradable plastic material furthercomprises a silicate, said silicate taking the form of particles havingan average diameter of 50 μm or less; and wherein said compound reactiveto active hydrogen comprises a bridging agent having a carbodiimidegroup comprising diisopropylcarbodiimide.
 2. The biodegradable plasticmaterial according to claim 1, wherein the acid value of saidbiodegradable plastic material treated with said compound reactive toactive hydrogen is 0.5 or less.
 3. The biodegradable plastic materialaccording to claim 1, wherein after said biodegradable plastic materialis subjected to aging for 48 hours at 80° C. and 80% relative humidity,an increase in acid value and a decrease in molecular weight of saidbiodegradable plastic material are 0.2 or less and 10% or less,respectively.
 4. The biodegradable plastic material according to claim1, wherein the active hydrogen is attributable to one or more atomicgroups comprising the polycaprolactone which are selected from the groupconsisting of a carboxyl group and a hydroxyl group.
 5. Thebiodegradable plastic material according to claim 1, wherein the silicondioxide content of said silicate is 50% or more.
 6. A biodegradableplastic molding, comprising a biodegradable plastic material treatedwith a compound reactive to active hydrogen contained in saidbiodegradable plastic material; wherein said biodegradable plasticmaterial comprises a polycaprolactone; wherein said biodegradableplastic material further comprises a silicate, said silicate taking theform of particles having an average diameter of 50 μm or less; andwherein said compound reactive to active hydrogen comprises a bridgingagent having a carbodiimide group comprising diisopropylcarbodiimide. 7.The biodegradable plastic molding according to claim 6, wherein saidbiodegradable plastic molding comprises a casing of an electricappliance.
 8. The biodegradable plastic molding according to claim 6,wherein the acid value of said biodegradable plastic material treatedwith the active hydrogen is 0.5 or less.
 9. The biodegradable plasticmolding according to claim 6, wherein after said biodegradable plasticmolding is subjected to aging at 80° C. and 80% relative humidity for 48hours, a rise in acid value and a decrease in molecular weight are 0.2or less and 10% or less, respectively.
 10. The biodegradable plasticmolding according to claim 6, wherein the active hydrogen isattributable to one or more atomic groups comprising thepolycaprolactone which are selected from the group consisting of acarboxyl group and a hydroxyl group.
 11. The biodegradable plasticmolding according to claim 6, wherein the silicon dioxide content ofsaid silicate is 50% or more.